Honeycomb Structured Porous Films Prepared by the Method of Breath Figure: History and Development

Solvent evaporation induced cooling of a solution surface will result in condensation of water vapor, which is known as breath figure. The condensed water droplets arrange normally into hexagonal packing to template the solution surface. After complete evaporation of solvent and water, hexagonally ordered porous array (breath figure array, BFA) can be left on the solute matrix by the imprints of the water droplets. An optimal BFA can be obtained by adjusting the controlling factors in a breath figure fabrication such as solvent, water vapor and material. The solvent is usually volatile organic solvent, and the water vapor can be dynamic or static; the solute can be homopolymer, block copolymer, polymer blend, polymer/additive mixture, polymer/inorganic hybrid or even pure nano particles. At the same time, hierarchically ordered structural patterns can be fabricated with such materials as building blocks by combining breath figure method with other microfabrication strategies. Moreover, specific fabrication procedures different from typical breath figure condition can be used for particular preparations. Progress in this field is summarized and discussed. Especially, some applications and post treatments of BFAs are introduced too.